Kontact on Debian

When coding at Kontact you normally don't have to care a lot about dependencies in between the different KDE Pim packages, because there are great tools available already. kdesrc-build finds a solution to build all KDE Pim packages in the correct order. The Kde Pim docker image gives you an environment with all dependencies preinstalled, so you can start hacking on KDE Pim directly.

While hacking on master is nice, most users are not using master on their computers in daily life. To reach the users, distributions need to compile and ship KDE Pim. I am active within Debian and would like to make the newest version of KDE Pim available to Debian users. Because Qt deprecated Qt Webkit within Qt 5.5 KDE Pim had to switch from Qt Webkit to Qt WebEngine. Unfortunately Qt WebEngine wasn't available in Debian, so I had to package Qt WebEngine for Debian before packaging KDE Pim for Debian. Qt WebEngine itself is a beast to package. It was only possible to package Qt WebEngine for the last stable release named "Stretch" in time with the help of others of the Debian Qt/KDE mainatiners especially Scarlett Clark, Dmitry Shachnev and Simon Quigley, and we could only upload it some hours before the deep freeze. So if you have asked yourself why Debian doesn't ship 16.08 within their last stable release, this is the answer. The missing dependency for KDE Pim named Qt WebEngine.
There is a second consequence of the switch: Kontact will only be available for those architectures that are supported by Qt WebEngine. Of 19 supported architectures for 16.04, we can only support five architectures in future.

Now after Debian has woken up again from its slumber, we first had to update Qt and KDE Frameworks. After the first attempt at packaging KDE Pim 17.08.0, that was released for experimental, we are now finally reaching the point where we can package and deliver KDE Pim 17.08.3 to Debian unstable. Because Pino Toscano and I had time we started packaging it and stumbled across the issue of having to package 58 source packages, all dependent on each other. Keep in mind all packaging work is not a oneman or twoman show, mostly all in the Qt/KDE Debian mantainers are involved somehow. Either by putting their name under a upload or by being available via IRC, mail and answering questions, making jokes or doing what so ever. Jonathan Riddell visualized the dependencies for KDE Pim 16.08 with graphviz. But KDE Pim is a fast moving target, and I wanted to make my own graphs and make them more useful for packaging.

Full dependency graph for KDE Pim 17.08

The dependencies you see on this graph are created out of the Build dependencies within Debian for KDE Pim 17.08. I stripped out every dependency that isn't part of KDE Pim. In contrast to Jonathan, I made the arrows from dependency to package. So the starting point of the arrow is the dependency and it is pointing to the packages that can be built from it. The green colour shows you packages that have no dependency inside KDE Pim. The blue indicates packages with nothing depending on them. But to be honest, neither Jonathan's nor my graph tells me any more than they do you. They are simply too convoluted. The only thing these graphs make apparent is that packaging KDE Pim is a very complex task :D

But fortunately we can simplify the graphs. For packaging, I'm not interested in "every" dependency, but only in "new" ones. That means, if a <package> depends on a,b and c, and b depends on a, than I know: Okay, I need to package b and c before <package> and a before b. I would call a an implicit dependency of <package>. Here again in a dot style syntax:

a -> <package>
b -> <package>
c -> <package>
a -> b

can be simplified to:

b -> <package>
c -> <package>
a -> b

With this quite simple rule to strip all implicit dependencies out of the graph we end up with a more useful one:

Simplified dependency graph for KDE Pim 17.08

(You can find the dot file and the code to create such a graph at pkg-kde.alioth.debian.org)

At least this is a lot easier to consume and create a package ordering from. But still it looks scary. So I came up with the idea to define tiers, influenced by the tier model in KDE Frameworks. I defined one tier as the maximum set of packages that are independent from each other and only depend on lower tiers:

Build tiers for KDE Pim 17.08 (The dot file and the code to create such a graph you can find at pkg-kde.alioth.debian.org)

Additionally I only show the dependencies, from the last tier to the current one. So a dependency from tier 0 -> tier 1 but not from tier 0 -> tier 2. That's why it looks like nothing depends on kdav or ktnef. But the ellipse shape tells you, that in higher tiers something depends on them. The lightblue diamond shaped ones in contrast indicating, nothing depending on them anymore. So here you can see the "hotpath" for dependencies. This shows that the bottleneck is libkdepim->pimcommon. Interestingly this is also, more or less, the border between the former split of kdepimlibs and kdepim during KDE SC 4 times.
I think this is a useful visualization of the dependencies and may be a starting point to define a goal, what the dependencies should look like.

You also may ask yourself why an application needs so much more tiers than complete KDE Frameworks? Well, the third tier of KDE Frameworks is more of a collection for leftovers that don't reach tier 1 or tier 2. See the definition of tier 3 is: "Tier 3 Frameworks can depend only on other Tier 3 Frameworks, Tier 2 Frameworks, Tier 1 Frameworks, Qt official frameworks, or other system libraries.". The relevant part is that a framework tier 3 can depend on other tier 3 frameworks. If you use my tier definition in contrast, then you end up with more than ten tiers for KDE Frameworks, too.

After building all of these nice graphs for Debian, I wanted to see if I could create such graphs for KDE Pim directly. As KDE is mostly using the kde-build-metadata.git for documenting dependencies I updated my scripts to create graphs from this data directly:

Simplified dependency graph for for KDE Pim 17.12 Build tiers for KDE Pim 17.12

(the code to build the graphs yourselves is available here: kde-dev-scripts.git/pim-build-deps-graphs.py)

In detail this graph looks different and not just because of the version difference (17.08 vs. master). I think we need to update the dependencies data. This also may explain why sometimes kdesrc-build don't manage it to compile complete KDE Pim in the first run.

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